Drawing and heat relaxing nylon yarn



' DRAWING AND HEAT RELAXING NYLON YARN 2 Sheets-Sheet 1 Filed Dec. 18.1968 INVENTORIS E L. LARKJIN' I w.T. HULL TTORNE 1970 F. LARKIN ETAL3,493,646

DRAWING AND HEAT RELAXING NYLON YARN 2 Sheets-Sheet 2 Filed Dec. 18,1968 INVENTORS F L LARKlN W-T. HULL United States Patent 3,493,646DRAWING AND HEAT RELAXING NYLON YARN Frank L. Larkin, Greenville, S.C.,and William T. Hull, Jr., Memphis, Tenn., assignors to Monsanto Company,St. Louis, Mo., a corporation of Delaware Continuation-impart ofapplication Ser. No. 587,597, Oct. 18, 1966. This application Dec. 18,1968, Ser. No. 784,731

Int. Cl. D02h N22 US. Cl. 264-290 2 Claims ABSTRACT OF THE DISCLOSUREDrawn nylon-66 yarn is relaxed by sliding contact in two or three passesover a surface heated to 140 C.225 C. The duration of contact in eachpass is between 0.005 and 0.1 second, and the yarn is under a tension ofbetween 0.05 and 0.60 gram per denier (g.p.d.) during each pass. Theyarn is cooled to a temperature less than 130 C. after each contact withthe heated surface.

This is a continuation-in-part of our co-pending application Ser. No.587,597, filed Oct. 18, 1966 (now forfeited); which application was acontinuation-in-part of application Ser. No. 318,150, filed Oct. 21,1963 (now abandoned); which application was a continuation-in-part ofapplication Ser. No. 241,997, filed Dec. 3, 1962 (now abandoned).

This invention relates to treatment of nylon-66 filaments. Moreparticularly, the invention relates to a process for relaxing nylonfilaments so that they have a lesser tendency to contractlongitudinally.

As is well known, nylon-66 filaments after being melt spun haverelatively low tensile strength and low molecular orientation, and mustbe drawn to increase the strength. The filaments are placed underconsiderable stress during the drawing operation. Most of this stress isrelieved in the form of an immediate partial elastic recovery when thetension on the filaments is first reduced. The immediate partial elasticrecovery ordinarily occurs between the drawing device and the take-updevice by significantly reducing the tension on the filaments at thispoint in the drawing operation. Usually, this reduction in length mayvary from four to eight percent of the length of the drawn filaments,depending upon processing conditions employed.

In addition to the tendency of the filaments to contract quickly afterbeing drawn, the filaments have a latent overstrain that is slow to berelieved at room temperature. It may take as long as twenty-four hoursat room temperature to relieve this strain completely even when thefilaments are under little or no tension. It has long been recognizedthat relief of latent strain can be hastened by relaxing the nylonfilaments at elevated temperatures which cause shrinking of thefilaments by an additional amount. This hot relaxing has beenaccomplished by steaming the filaments or by applying heat to thefilaments in other ways immediately after drawing and before packageformation. Unfortunately, complete relaxation of the filamentsordinarily is gained at the expense of obtaining filaments having anundesirably low initial modulus. In recent times, methods and apparatushave been disclosed whereby freshly drawn nylon filaments are hotrelaxed under controlled conditions without considerable lowering of theinitial modulus thereof. The known methods and apparatus for doing thisrequire extensive alteration of existing nylon drawing equipment or donot permit accurate control of the filaments during hot relaxationthereof so as to produce filaments of optimum physical properties.

It is an object of the present invention to provide an improved processsfor producing nylon-66 filaments hav- "ice ing a reduced tendency tocontract in length with no sacrifice of initial modulus, and having asatisfactory elongation-to-break.

Another object of the present invention is to provide new and usefulapparatus for stretching and hot relaxing nylon filaments.

Other objects will be apparent from the following detailed description.

Generally, the objects of the invention are achieved by drawing nylon-66yarn at a temperature of -190" C., and relaxing the yarn by slidingcontact in two or three passes over a non-rotatable relaxing pin heatedto a temperature between C. and about 225 C., preferably between C. and195 C. The circumference of the relaxing pin should be such that theyarn contacts the pin between 0.005 second and 0.1 second in each pass,and the tension on the yarn during the relaxing step should be between0.05 and 0.60 gram per denier (g.p.d.). The yarn is cooled to atemperature less than 130 C. after each pass over the pin. The yarn isthen taken up at a tension between 0.05 and 0.60 gram per denier, asprovided by a take-up speed immediately after the yarn is drawn.

Suitable apparatus for performing the invention is illustrated inFIGURES 1 and 2 which are schematic perspective views with principalparts in location, illustrating preferred yarn lacing arrangements.

Referring now to FIGURE 1, undrawn nylon-66 yarn 10 is supplied from asuitable yarn source 11 to a pair of driven nip rolls 12 and 13. Theyarn next makes one or more wraps around a fixed drawn pin 14, orequivalent yarn braking means. Pin 14 can be heated if necessary toraise the temperature of yarn to the desired range of 110 C.- 0.,although heating of the pin is usually not necessary.

Yarn 10 next passes several wraps around draw roll 15 and separator roll16, to afford sufiicient traction to draw the yarn. As illustrated, theaxes of rolls 15 and 16 are slightly skewed to permit separation ofadjacent wraps. At point 17 the yarn normally has a temperature of about110 to 190 C. and is under a high tension. As the yarn progresses alongrolls 15- and 16 the yarn temperature decreases to about 40120 C. andthe tension on the yarn is reduced with each succeeding wrap.

A non-rotatable heated relaxing pin 18 is positioned adjacent draw roll15, and has its axis slightly skewed with respect to the axis of drawroll 15, to prevent superimposition of adjacent wraps of yarn. Pin 18may be heated electrically by current supplied through conductors 20 ifdesired, although pin 18 may be heated in other known ways. The yarnafter contacting draw roll 15 six times is wrapped about relaxing pin18, then around draw roll 15 and back around relaxing pin 18, so thatthe yarn makes two wraps about relaxing pin 18. As illustrated, the yarnmay pass over separator roll 16 to a suitable take-up mechanism 23.

The yarn is withdrawn by take-up mechanism 23 at between 4 and 12% lessthan the yarn speed at point 17. With the string-up illustrated in thedrawing, this will provide yarn tension (as the yarn contacts pin 18) ofbetween 0.05 and 0.60 gram per denier.

The string-up of the apparatus in FIGURE 2 is identical to that shown inFIGURE 1 except that the yarn after its initial contact with pin 18 ispassed around separator roll 16 before coming into contact with roll 15.This provides a longer path for the yarn to travel between its contactswith heated pin 18. This arrangement is preferred at faster yarntreating speeds in order to provide adequate cooling of the yarn betweenits contact periods with pin 18.

EXAM'PLE In the apparatus of FIGURE 1, a 34-filament nylon-66 yarn, spunfrom a polymer having a relative viscosity of 43 and having a spundenier of 176, was removed from a spin bobbin and advanced by feed rolls12 and 13. The yarn was wrapped two times around draw pin 14 and thenwas wrapped five times about draw roll 15 and separator roll 16, asillustrated in the drawing. The speed of feed rolls 12 and 13 wasadjusted relative to the speed of draw roll 15 to provide a draw ratioof 2.74 while driving roll 15 at a peripheral speed of 840 yards perminute. The yarn as it left engagement with draw pin 14 was under atension of about 170 grams. As the yarn progressed around rolls 15 and16, the tension decreased to about 137 grams at the fifth wrap. The yarnwas then looped back around heating pin 18. The external temperature ofpin 18 was 180 C. and its diameter was two inches. At point 21 (justbefore engagement with pin 18), the tension was 4 grams and at point 22(after engagement with pin 18) the tension was 12 grams.

The yarn was wrapped around draw roll 15 and looped back around relaxingpin 18. Just before re-engagement with pin 18 the tension was 4 grams,and after re-engagement with the pin the tension was 11 grams. The speedof the take-up mechanism was regulated to provide a winding tension of 9grams at point 24. The resulting yarn had an initial modulus of 28.0grams per denier, with an elongation-to-break of 35.4% and a residualboiling water shrinkage of 4.8%.

Relative viscosity is determined by the method described in US PatentNo. 2,385,890.

For determining the residual yarn shrinkage, a skein of yarn is placedin boiling water for 60 minutes and then is hung up to dry fortwenty-four hours under a load of 0.1 g.p.d. Percent shrinkage is theinitial length of yarn minus the length thereof after boiling divided bythe initial length of the yarn times one hundred.

Initial modulus is defined as a ratio of change in stress to strain inthe first linear portion of a stress-strain curve. The ratio iscalculated from the stress, expressed in force per unit linear density,and the strain expressed as percent elongation. As the strain isexpressed in terms of elongation, the modulus equals one hundred timesthe quotient (stress/strain). The modulus is determined at 1 /2 percentelongation based on the slope of the curve at this percentage. Theinitial modulus is obtained using the Instron Tensile Tester (Model TTB,supplied by Instron Engineering Corporation, Quincy, Mass.), whichstretches the yarn at a constant rate of elongation. All yarn isconditioned for seven days at 75 F., 72% relative humidity prior totesting. The specific settings used on the Instron Tensile Tester were:Load Cell B (500 gm. setting); sample length of 25 cm.; cross-head speed15.2 centimeters per minute; and chart speed 24.3 centimeters perminute. From the stress-strain curve, the stress is measured graphicallyat 1 /2 percent elongation on the initial linear portion of thestress-strain curve; and the modulus is calculated at one hundred timesthis value, divided by the denier of the yarn sample.

The elongation-to-break is that percentage by which the drawn andpackaged yarn can be elongated before the yarn breaks. This property ismeasured using the same Instron settings as above. For ordinary textileyarns, an elongation of at least 27%, and preferably 30% or more, ispresently required for commercial acceptance. With nylon- 66 yarn it hasbeen discovered that elongation-to-break decreases and shrinkage atfirst decreases and then increases, with an increase in the number ofwraps around heated pin 18, as shown in Table 1. In addition, tensilestrength and denier of nylon-66 yarn decrease linearly with anincreasing number of wraps. In Table l, the process as described in theexample was followed, except that the number of wraps around pin 18 wasvaried as indicated, and that the take-up speed was adjusted to provide8 grams wi d ng nsion.

TABLE 1 Wraps 1 2 3 4 Modulus, g.p.d 26. 9 28.0 29. 1 30. 3Elongation-to-break, percent 36. 5 35. 4 33. 2 27. 2 Shrinkage, percent4. 5 4. 8 5. 1 5. 4

This decrease in elongation-to-break would be even more objectionablewith yarns which are drawn to a higher degree, such as industrial yarns.Although modulus increases with increasing wraps, use of more than threewraps about pin 18 produces unacceptably high shrinkage and (moreimportantly) unacceptably low elongation-tobreak and breaking strength.

In summary, it has been found that with nylon-66 yarn, relaxing the yarnat a tension less than 0.05 gram per denier yields an unacceptably lowinitial modulus, while relaxing at a tension more than 0.60 gram perdenier produces an unacceptably high shrinkage. Furthermore, a singlepass of the yarn over relaxing pin 18 is usually not feasible since itdoes not normally provide a sufiiciently high initial modulus. More thanthree passes of the yarn over pin 18 produces increased shrinkage andreduced elongation-to-break. Accordingly, optimum results are achievedwith either two or three Wraps are taken about pin 18.

It will thus be seen that the objects set forth above, among those madeapparent from the preceding description, are efliciently attained and,since certain changes may be made in carrying out the above process andin the constructions set forth without departing from the scope of theinvention, it is intended that all matter contained in the abovedescription or shown in the accompanying drawings shall be interpretedas illustrative and not in a limit- 111g sense.

Having described our invention, what we claim as new and desire tosecure by Letters Patent is:

1. A process for producing relaxed drawn continuous filament nylon-66yarn, comprising in combination the steps of:

(a) drawing said yarn several times its original length at a temperatureof from about 190 C.,

(b) cooling said yarn to about 40130 C.,

(c) relaxing said yarn by:

( 1) heating said yarn a plurality less than four times by slidingcon-tact for periods between 0.005 and 0.1 second in each pass with asurface heated to C. and 225 C., and

(2) cooling said yarn to a temperature less than about 130 C. after eachcontact with said surface,

(d) taking up said yarn in package form at a speed between 4% and 12%less than the speed immediately after said yarn is drawn,

(e) the yarn tension during steps (c) and (d) being between 0.05 and0.60 gram per denier.

2. The process defined in claim 1, wherein said surface is heated to atemperature between C. and C.

References Cited UNITED STATES PATENTS 2,859,472 11/1958 Wincklhofer.3,161,913 12/1964 Pound. 3,287,888 11/1966 Chidgey. 3,295,182 1/1967Robbins et a1. 3,441,642 4/1969 Engelman et al. 264237 FOREIGN PATENTS907,754 10/1962 Great Britain.

JULIUS FROME, Primary Examiner HERBERT MINTZ, Assistant Examiner US. Cl.X.R.

